Crystallizing apparatus



Nnv. 22, 1960 E. A. ZDANSKY ETAI. 2,960,843

CRYSTALLIZING APPARATUS Filed Sept. 2:5, 1957 2 Sheets- Sheet 1 Inventors Nov. 22,, 1960 E. A. ZDANSKY ETA]. 2,960,843

I CRYSTALLIZING APPARATUS Filed Sept. 23, 1957 2 Sheets-Sheet 2 l I Ii Wall/Z717 A IE lmw Aff y United States Patent CRYSTALLIZING APPARATUS Ewald A. Zdansky and Heinrich H. Getfcken, both of Monthey, Valais, Switzerland Filed Sept. 23, 1957, Ser. No. 685,512 Claims priority, application Germany Sept. 22, 1956 13 Claims. (Cl. 62-123) The present invention relates to crystallizing apparatus.

More particularly, the present invention relates to crystallizing apparatus where precipitation occurs due to cooling of a solution wherein the solute is less soluble in the solvent at lower temperatures than at higher temperatures. For example, the invention may be used with aqueous sodium sulfate, with dicyandiamide solution, etc.

crystallizing apparatus of the above type generally includes a precipitation tower in which a plurality of cooling tubes are located, these tubes extending longitudinally along the interior of the tower. Such apparatus conventionally includes doctor blades which are reciprocated along the exterior of the cooling tubes for scraping from the outer surface thereof crystals which adhere thereto, and the necessity of such doctor blades renders the apparatus useful only for a few specialized applications. Moreover, such a crystallizing apparatus has undesirable currents circulating through the solution in the precipitation tower. These currents result from the fact that the hot mother liquor introduced into the top of the precipitation tower has a greater specific weight than the depleted mother liquor within the tower. Thus, a part of the heavier mother liquor falls downwardly through the solution in the tower to the crystals at the bottom thereof and causes these crystals to undesirably fuse together in clusters.

One of the objects of the present invention is to provide a crystallizing apparatus which does not require any doctor blades or the like and which at the same time is capable of preventing crystals from adhering to the outer surfaces of the cooling tubes.

Another object of the present invention is to provide a crystallizing apparatus which will guarantee that there are no undesirable circulating currents of the above type.

A further object of the present invention is to provide a crystallizing apparatus composed of relatively simple, ruggedly constructed parts which are very reliable in operation and which are capable of being quickly and easily assembled and disassembled.

With the above objects in view the present invention includes in a crystallizing apparatus a precipitation tower, a plurality of cooling tubes extending longitudinally along the interior of the precipitation tower, and a plurality of partitions distributed along the tower, extending across the interior thereof, and dividing the tower into a plurality of successive chambers, these partitions being formed with cutouts through which the cooling tubes as well as the solution within the tower pass. The tower has a bottom discharge outlet, and a valve means is located at this discharge outlet for opening and closing the same, and a valve operating means cooperates With the valve means for periodically opening the same and maintaining the same open for a predetermined length of time, so that the materials within the tower move pulsatingly downwardly through and out of the same.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both 2,960,843 Patented Nov. 22, 1960 as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

Fig. l is a partly diagrammatic, partly sectional illustration of the entire crystallizing apparatus;

Fig. 2 is a fragmentary sectional view on an enlarged scale of zone II of Fig. 1;

Fig. 3 is a fragmentary sectional view on an enlarged scale of zone III of Fig. 1;

Fig. 4 is a sectional plan view taken along line IV--IV of Fig. 3 in the direction of the arrows;

Fig. 5 is a fragmentary sectional elevational view of a different embodiment of structure shown in Fig. 2; and

Fig. 6 schematically illustrates the operation of the crystallizing apparatus with respect to the manner in which crystals are prevented from adhering to the outer surfaces of the cooling tubes and with respect to the manner in which turbulence is created in the boundary layers of the cooling fluid within the cooling tubes.

As may be seen from Fig. 1, the crystallizing apparatus of the invention includes a cylindrical precipitation tower 1, this precipitation tower fixedly carrying a support ring 2 which rests upon a transverse stationary support 3, the latter being formed with an opening through which the tower 1 passes and the ring 2 resting upon the support 3. The total height of the apparatus may be approximately 6-7 meters.

A plurality of cylindrical cooling tubes 4 are suspended within the tower 1, extend longitudinally along the interior thereof, and are parallel to each other as well as with respect to the axis of the tower about which the cooling tubes 4 are distributed. A cooling fluid rises upwardly within the cooling tubes 4 as shown by the straight arrows in Fig. 1 and Fig. 2. The solution which is cooled so as to have the solute therein precipitated therefrom moves in countercurrent to the upwardly moving cooling fluid within the cooling tubes, and the downward movement of this solution is indicated by the wavy arrows at the lower part of Fig. 1 and Fig. 2. The solution is derived from a dissolution container 5 which communicates with a pump 5a which draws the solution from the container 5 and delivers it to an entrance conduit 6 carried by and communicating with the interior of a jacket 7 which surrounds and is fixed to the outer surface of the tower 1, in the manner shown most clearly in Fig. 2. This jacket defines with the tower 1 an annular chamber 9 to which the mother liquor is delivered by the pump 5a through the conduit 6, and the jacket 7 is provided with an overflow conduit 8 through which the excess solution flows back to the container 5. The wall of the tower 1 is formed with a plurality of openings 10 arranged along a circle adjacent the bottom end of the chamber 9, and the mother liquor flows from the chamber 9 through the openings 10 into the interior of the precipitation tower 1, as is indicated in Fig. 2. The solution is then cooled in stepwise fashion within the tower 1 as the solution moves downwardly along the interior thereof, as will be apparent from the description which follows.

The tower 1 is provided at its bottom end with a discharge outlet controlled by a non-return valve 11 which is movable between open and closed positions for respectively opening and closing the discharge outlet, and when the valve 11 is in its open position the crystal sludge at the bottom of the precipitation tower 1 together with the depleted mother liquor flow from the tower to a centrifuge 13. The non-return valve 11 has a valve stem 12 connected with a piston within a pneumatic cylinder 14, and at intervals of at least 2 seconds and which may range from 2 to 20 seconds although practically the range will be from 2 to seconds the valve is opened and maintained open for a period of 0.5-1 second, so that the exhausted mother liquor together with the crystals flow out of the tower in a pulsating fashion. Although a rotary slide valve could be used for periodically opening and closing the discharge outlet of the tower, it is preferred to use the non-return valve 11 which is operated by the pneumatic means 14 so that the discharge outlet is suddenly opened and suddenly closed at the predetermined intervals. The pneumatic means 14 may be controlled by impulses derived from an electronic impulse transmitter cooperating with a magnetic three-way valve of known construction. This three-way valve connects the supply line p which delivers air under pressure to the cylinder 14 alternately with a source of compressed air and with the outer atmosphere.

As may be seen from Figs. 3 and 4, there may be, for example, eight cooling tubes 4 in the tower 1 arranged in a circle about the axis of the tower. Referring to Fig. 2, it will be seen that each cooling tube 4 has an upper section 411 whose wall thickness is greater than the next lower section of the cooling tube, and each cooling tube is made up of a series of such sections with each section of a wall thickness greater than the next lower section. As may be seen from Figs. 3 and 5, the bottom end of each cooling tube 4 is closed by a hollow substantially conical member 20 having a wall thickness greater than that of the cooling tube itself. These closure members 20 may be welded into the bottom ends of the cooling tubes, respectively. A supply tube 21 extends axially along the interior of each cooling tube 4 for supplying a cooling fluid thereto, and each supply tube 21 has been a bottom open end cooperating with the hollow interior of the closure member 20 for providing in the interior of each cooling tube 4 a cooling liquid which rises upwardly along the interior of the cooling tube 4 at the exterior of the supply tube 21 therein. Thus, the cooling liquid is introduced into the bottom end of each cooling tube and rises slowly upward along the interior thereof. The cooling liquid discharges through the top open ends of the cooling tubes 4 into a chamber 22 carried by the tower 1 at its top end, and this chamber 22 has a bottom annular wall 41 fixed to the outer surface of the tower 1 beneath the top end thereof and carrying an elbow 23 through which the discharged cooling liquid flows in the direction of arrow F as indicated in Fig. 2.

According to the present invention the tower 1 is provided with a plurality of partitions located at the elevations indicated by the horizontal dotted lines in Fig. 1, these partitions dividing the interior of the tower into a plurality of successive chambers -19 indicated in Fig. 1. These partitions are formed with openings through which the cooling tubes 4 pass, and the partitions provide at their openings relatively narrow annular gaps around the cooling tubes through which the solution flows. The partitions may be in the form of solid or apertured horizontally arranged metal sheets, for example, but preferably they are of frusto-conical configuration having their smaller ends located at a lower elevation than their larger ends (Fig. 3), and at their smaller ends the partitions are formed with openings, respectively, for the passage of somewhat larger crystal agglomerates.

The cooling tubes 4 are carried, as may be seen from Fig. 2, by a lower head member 24 and an upper head member 25 cooperates with the head member 24 for holding the coling tubes at their top ends. The lower head member 24 extends across the top of the tower 1 and is provided with a plurality of tubular portions 26 through which the top ends of the cooling tubes 4 respectively pass, and the upper head member 25 is formed with a plurality of openings 27 aligned with the tubular members 26 of the lower head member 24. The cooling tubes 4 flare outwardly at their top ends, respectively, and a sleeve means is fixed to the top end of each cooling tube. This sleeve means is in the form of an Outer sleeve member 28 engaging the outer surface of each cooling tube at its top end and an inner sleeve member 29 extending into the interior of each cooling tube at its top end, as indicated in Fig. 2. The sleeves 28 and 29 are provided with outwardly directed annular flanges which are welded to each other and to the top end of each cooling tube 4. The flange at the top of each sleeve member 28 rests on the top end of a tubular portion 26, as indicated in Fig. 2. The flange of the sleeve member 29 is engaged by the under side of the head member 25, and the sleeve means is thus gripped at its flanges between the head members 24 and 25 both of which may be dished, if desired. The head member 24 fixedly carries a plurality of angle members 30 distributed uniformly about the periphery of the head member 24, and there may be, for example, eight angle members 30. These angle members respectively carry screws 31 which cooperate with the ring 32 to urge the latter downwardly toward the outer periphery of the upper head member 25, an elastic ring 33 being interposed between the ring 32 and the outer periphery of the upper head member 25. Thus, the screw means 31 serves to clamp the head members 24 and 25 together with the flange means 28, 29 gripped therebetween. A sealing ring 34, which may be in the form of an O-ring is located in an annular groove formed at the outer surface of each sleeve member 28 and fluidtightly engages the inner surface of each tubular portion 26 of the lower head member 24. It is apparent that the screw means 31 may be unscrewed so as to permit the upper head member 25 to be removed, and then the several cooling tubes 4 may be removed from the tower 1 and exchanged.

Furthermore, if necessary the cooling tubes 4 may be placed under the influence of a hammer action. For this purpose the upper head member 25 is provided at its central portion with an anvil 35 and the head member 25 is strengthened by ribs 36 extending radially from the anvil 35 and respectively located substantially midway between the axes of the several cooling tubes 4. Thus, in the illustrated example there are eight ribs 36. A pneumatic hammer apparatus 37 is located over the anvil 35 and is carried by the frusto-conical jacket member 38 which defines the chamber 22. The hammer apparatus 37 includes a hammer 39 which strikes the anvil 35 approximately one each second with a great force on the order of, for example, 10-20 mkg. see. In practice, the best frequency for the hammer blows is empirically determined in each case.

A ring 42 is welded to the top end of the tower 1, and the second ring 41 is welded to the exterior surface of the tower 1 just beneath the ring 42, this ring 41 forming the lower limit of the chamber 22 and carrying the elbow 23, as was described above. Thus, the ring 41 together with the jacket 38 defines the chamber 22 through which the cooling fluid discharges. The lower head member 24 is provided with a downwardly directed groove into which the ring 42 extends, and an annular hollow ring 43 of rubber or the like, or a similar springy element of annular configuration, is located in this groove on ring 42. This way a resilient support means is carried by the tower 1 for supporting the several tubes 4 for yieldable downward movement. The hollow interior of the resilient tube 43 may communicate through a nonreturn valve with a source of compressed air, and the compressed air may be maintained at a constant adjustable pressure of, for example, 1-2 atmospheres. The annular ring 43 acts similarly to a tire as an elastic support for the head members 24 and 25, so that the latter together with the cooling tubes 4 may move downwardly in the direction of arrow A of Fig, 2 through a distance of approximately 0.5-2 mm. The cooling tubes 4 are thus moved very suddenly in a downward direction together with the head members 24 and 25.

Instead of the above-described connection between the head frlembers and the cooling tubes, an arrangement as shown in Fig. 5 may be used, according to which the individual cooling tubes 4 are respectively supported by coil springs 44. In this embodiment the lower head member 24a is provided with an outwardly directed annular flange fixedly connected by suitable screws or the like with the flange 42a fixed to the top end of the tower 1, and the springs 44 bear at their bottom ends on the head member 24a. The top ends of the springs 44 bear against the flanges of the outer sleeve members 28. The upper head member 25a of Fig. 5 rests directly on the inner sleeve members 29 and the force of the hammer blows received by the anvil 35a are transmitted through the sleeve members 29 to the cooling tubes 4 so that the latter also are periodically moved suddenly in the direction of arrow A of Fig. 5.

Fig. 6 illustrates on an extremely large scale a section of a right side wall of a cooling tube 4. It is assumed that a crystal accumulation 45 has started to adhere to the outer surface of the cooling tube 4. When this cooling tube 4 is suddenly urged downwardly in the direction of arrow A of Fig. 6 by the hammer blow, there is created a very' strong shearing force between the practically stationary body of liquid S and the outer surface of the cooling tube 4, and this shearing action tears the crystal accumulation 45 from the outer surface of the tube 4 and causes the accumulation 45 to move somewhat in the direction of the curved arrow of Fig. 6 into the solution S. This process repeats itself at each blow of the hammer 38 at millions of outer surface points of each cooling tube 4, so that the detached crystals distribute themselves throughout the entire solution in the f interior of the precipitation tower 1.

The above-described detaching of a crystal 45 from the 'cooling tube 4 takes place with a probability which becomes smaller as the smoothness of the outer surface of the cooling tube 4 increases. Therefore, the outer surfaces of the cooling tubes are highly polished and for this purpose they are also, if desired, nickeled or chromed.

Furthermore, the separation of the crystals from the outer surface of the cooling tubes 4 requires a certain minimum hammer force which depends upon the particular solution within the tower and the properties of the outer surfaces of the cooling tubes. It is intended that the hammer blow will cause the tubes 4 to receive a considerable acceleration downwardly and must have a minimum tendency to bend the tubes 4, in order that the energy of the hammer should not be converted into a bending movement, Thus, it is essential that the tubes 4 be light, but nevertheless sufiiciently stiff so that they will not bend, and for this reason the tubes 4 preferably are each composed of a series of sections of different wall thickness with the thickness of each section being greater than the thickness of the next lower section, as was described above. In this way the cooling tubes 4 have the smallest possible weight and the necessary rigidity.

The several supply tubes 21 which supply the cooling liquid to the interior of the cooling tubes 4 are carried by a hollow annular tube 50 which is supported by radial extensions passing through elastic sleeves 51 carried by the jacket 38. The radial extension 52 shown in Fig. 2 'is hollow so that it simultaneously serves as an inlet conduit through which the cooling liquid flows in the direction of arrow F of Fig. 2 into the interior of the hollow ring 50, and the interior of the ring 50 communi cates with the interior of the tubes 21 so that the cooling fluid fiows from the ring 50 downwardly along the several cooling tubes 21. Thus, the several supply tubes 21 are suspended independently of the periodically vibrating cooling tubes 4.

In the interior of the cooling tubes 4 which are of relatively large diameter the cooling liquid moves upwardly at a relatively slow rate, this cooling liquid being water, for example. Therefore, the flow remains laminar, and as a result stagnant boundary layers of the cooling liquid form at the inner surface of the cooling tubes 4 and reduce the rate of heat transfer. In order to break up these boundary layers air bubbles are continuously supplied to the interior of the cooling tubes 4 and are directed upwardly along the inner surfaces thereof so that stagnant boundary layers cannot remain at these inner surfaces. The compressed air for these bubbles is supplied through the annular tube 53 located just over the tube 50, and carried by the latter, the tube 53 communicating with an unillustrated source of compressed air. The tube 53 communicates with a plurality of nozzles 54 which extends downwardly into the interior of the tube 50 and which have discharge ends respectively located at the entrance ends of the supply tubes 21, as indicated most clearly in Fig. 2. The cooling water which flows quickly into the inlet ends of the supply tubes 21 carries air bubbles from the nozzles 54 downwardly along the tubes 21 to the bottom end of the cooling tubes 4 where the cooling liquid together With the air bubbles are distributed in the manner shown by the arrows at the lower end of Fig. 5 just above the closure member 20. A distributor disc 55 made of rubber, for example, is carried by the bottom end of each supply tube 21 in the interior of each cooling tube 4 and has an outer serrated periphery located next to the inner surface of the cooling tube 4 so that the air bubbles together with the cooling liquid is compelled to flow upwardly at the inner surface of cooling tube 4. A plurality of additional distributor discs 55a of the same construction as distributor disc 55 are carried by each supply tube 21 above the lower disc 55, and the several discs 55a and 55 are spaced from each other by a distance of approximately 2050 cm. Thus, the air bubbles as well as the cooling liquid are repeatedly distributed at the inner surface of each cooling tube.

As is apparent from Figs. 3 and 4 the partitions are preferably, according to the present invention, in the form of fmstoconical sheet metal elements 56 fixed at their outer peripheries to angle rings 57 which in turn are fixed to the inner surface of the tower. Fig. 3 shows a pair of such rings 57 and 57a carrying the partitions 56 and 56a, respectively, which define between themselves the lowermost chamber 19 of the tower 1. The several partitions 56 are formed at their smaller downwardly directed ends with openings 58, the openings 58 and 58a being shown in Fig. 3, and in addition the several partitions 56 are each formed with eight openings 59 through which the cooling tubes 4 respectively pass, openings 59 and 59a of the partitions 56 and 56a, respectively, being indicated in Fig. 3. The openings 59 are somewhat larger than the cooling tubes 4 so that an annular gap of a width of approximately 10 mm. surrounds each cooling tube 4 at each partition 59, and the solution flows through these gaps. Beneath each opening 58 each partition 56 carries a conical baffle member 60, the baflle members 60 and 6011 being shown in Fig. 3, and each partition 56 is provided with three radially extend ing rib members fixed to and extending downwardly from its lower surface and fixedly carrying each baffie 60, these ribs being distributed about the axis of the partition and spaced from each other by Thus, the solution which flows through the central openings 58, 58a. etc. is compelled by the baffles 60, 6001, etc. to flow radially toward the wall of the tower 1, and in this way a concentration of the downward flow at the central portion of. the tower is avoided.

Each time the substantially mushroom-shaped valve 11 is opened for a short period the entire liquid column within the tower 1 suddenly moves downwardly, and the cross section and time during which the valve 11 remains open are so chosen that the liquid column in the tower moves downwardly at each opening impulse of the valve approximately 5l00 mm. Thus, the liquid is compelled to flow through the openings 58 and the annular gaps 59 and a strong turbulence is provided. This process repeats itself each time the valve is opened and produces a strong flow along the exterior surface of the cooling tube 4 so that crystals which tend to adhere to the tubes 4 are detached therefrom and float in the solution. Furthermore, owing to the mixing effect of these flows no regions of elevated temperatures can become created within the chambers defined by the partitions 56. In a vertical direction the partitions divide the tower 1 into a plurality of overlying chambers which respectively have average temperatures which fall in a stepwise fashion from the top to the bottom of the tower.

In many cases it is advisable to provide each partition 56 at the edge of the openings 58 and 59 thereof with a rubber ring 61 which extends inwardly to each opening by a distance of 0.52 cm., so that the opening 58 of each partition is provided with an inwardly extending elastic flexible lip, and the flexibility of each lip can be increased by providing each lip with radial slits 62 (Fig. 4).

The operating cycle of the valve 11 is preferably adjusted so that the valve is opened at least every two seconds and at the most every 20 seconds, and the duration of the downward impulse of the liquid in the tower, which is to say the duration of time during which the valve is maintained open at each cycle should be less than one second, for example, 0.5 second, and the valve is preferably opened and closed very quickly so that a sudden opening and a sudden closing is provided.

When dealing with certain types of solutions, the combination of the sudden downward movements of the body of liquid within the tower 1 with the highly polished outer surface of the cooling tubes 4 is suflicient to prevent crystals from adhering to the cooling tubes 4, so that in these cases the hammer action need not be used.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of crystallizing apparatus differing from the types described above.

While the invention has been illustrated and described as embodied in crystallizing-cooling apparatus, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In a crystallizing apparatus, in combination, a precipitation tower; a cooling tube extending longitudinally along the interior of said tower and having an outwardly flaring open top end portion; an inner sleeve member extending into the interior of said open top end portion of said cooling tube; an outer sleeve member engaging and surrounding the exterior of said open top end portion of said cooling tube, said inner and outer sleeve members being fixed to said cooling tube, and said outer sleeve member having an outwardly directed annular flange; resilient support means engaging said flange to yieldably resist downward movement of said sleeve members and cooling tube; and anvil means cooperating with said inner sleeve member for transmitting to the latter blows of a hammer for axially moving said cooling tube.

2. In a crystallizing apparatus, in combination, a precipitation tower; at least one cooling tube extending longitudinally along the interior of said tower and having a top open end portion; sleeve means fixed to said top end of said cooling tube and having an outwardly directed flange means; upper and lower head members respectively clamping said flange means therebetween; support means resiliently supporting said lower head member on said tower; and an anvil carried by said upper head member for transmitting blows of a hammer to said cooling tube.

3. In a crystallizing apparatus as defined in claim 1, said tube having a plurality of successive sections of different wall thickness, and each section having a wall thickness greater than the next lower section.

4. A crystallizing apparatus comprising, in combination, a precipitation tower having a bottom discharge outlet; a plurality of cooling tubes extending longitudinally along the interior of said precipitation tower; a plurality of partitions distributed along said tower, extending across the interior thereof, and dividing said tower into a plurality of chambers, said partitions being respectively formed with cutouts through which said cooling tubes pass and through which a solution in said tower moves toward the bottom discharge outlet of said tower; support means carried by said tower and resiliently supporting said tubes for yieldable movement downwardly toward the bottom end of said tower; hammer means cooperating with said tubes for periodically providing a downward force periodically moving said tubes downwardly in said tower to promote the detachment of crystals from the outer surfaces of said tubes; means carried by said tower for supplying cooling fluid to the interior of said cooling tubes and for discharging cooling fluid from the interior of said cooling tubes; valve means cooperating with said discharge outlet of said tower and movable between open and closed positions for respectively opening and closing said discharge outlet; and means cooperating with said valve means for periodically opening the same and for maintaining said valve means in its open position for a predetermined period of time.

5. In a crystallizing apparatus, in combination, a precipitation tower in which crystals are precipitated from a solution, the tower having a bottom discharge outlet; means communicating with the interior of said tower adjacent to the top thereof for filling said tower with a solution up to a preselected level adjacent the top of said tower and for maintaining said level substantially constant during operation of said tower; at least one cooling tube extending longitudinally along the interior of said tower for cooling a solution therein; means for passing a cooling fluid in upward direction through said tube; a plurality of partitions distributed along the length of the tower and extending across the interior thereof to divide the interior of said tower into a plurality of successive chambers, said partitions being respectively formed with cutouts through which said cooling tube passes and through which the solution may pass; valve means cooperating with said discharge outlet of said tower and movable between an open position opening said discharge outlet and a closed position closing said discharge outlet; and valve operating means cooperating with said valve means for automatically moving said valve means in a preselected sequence between its open and closed position during operation of the crystallizing apparatus, whereby the solution will move intermittently and with sudden acceleration and deceleration through said cutouts from the topmost to the lowermost of said chambers in a direction opposite to the direction the cooling fluid flows through said cooling tube creating thereby intermittent currents of the solution so as to prevent agglomeration of crystals in said cutouts and along the outer surface of said cooling tube.

6. An apparatus as defined in claim 5 in which said valve operating means rapidly moves said valve means between said open and closed position thereof to increase thereby acceleration and deceleration of the flow of solution through said cutouts.

7. An apparatus as defined in claim 5 in which each of said partitions has a substantially frustoconical configuration, having its larger peripheral end located next to the inner surface of said tower and having its smaller end located at a lower elevation than its large end, said smaller end of each partition being formed with an opening through which a solution in said tower passes.

8. An apparatus as defined in claim 7 and including a baflie carried by each partition beneath the opening at its smaller end for directing fluid passing downwardly through said opening in a direction transverse to the longitudinal axis of said tower.

9. An apparatus as defined in claim 7 and including an elastic flexible ring carried by each partition at said opening at said smaller end therof, said ring extending radially inwardly from the edge of the latter opening and providing each partition with a flexible lip.

10. An apparatus as defined in claim 9 in which said elastic ring being formed with radial slits extending from its inner periphery.

11. An apparatus as defined in claim 5 in which said cooling tube has a highly polished outer surface so as to facilitate removal of crystals forming on said outer surface by said currents created in the solution.

12. An apparatus as defined in claim 5 in which said cooling tube has a highly polished, chromed outer surface so as to facilitate removal of crystals forming on said outer surface by said current created in the solution.

13. An apparatus as defined in claim 5 in which said cooling fluid is a cooling liquid and means for circulating gas bubbles through said cooling liquid to prevent laminar flow of said cooling liquid through said cooling tube.

References Cited in the file of this patent UNITED STATES PATENTS 1,694,369 Burdick Dec. 11, 1928 1,780,267 Malone Nov. 4, 1930 1,880,925 Eissner Oct. 4, 1932 2,522,651 Van Vleck Sept. 19, 1950 2,682,155 Ayres June 29, 1954 2,723,534 Wilbushewich Nov. 15, 1955 2,734,345 Lawler Feb. 14, 1956 2,777,888 Hofi Jan. 15, 1957 2,790,309 Wenzelberger Apr. 30, 1957 2,790,493 Wenzelberger Apr. 30, 1957 2,800,001 Wenzelberger July 23, 1957 

